1. Field of the Invention
The present invention relates to an explosion proof motor robot assembly, and particularly to a high safety sealed type internal pressure explosion proof assembly.
2. Description of the Prior Art
In coating robots, built-up robots used under the explosion atmosphere and other working robots, there is a possible danger of explosion due to sparks or the like generated by wire breakage or motor breakdown. Prior art driving devices for these robots are of a so-called essentially safety explosion proof assembly which uses a hydraulic cylinder free from a possibility of occurrence of a spark. These hydraulic driving systems are inferior to driving mechanisms using an electric motor in the light of the fact that fine locating cannot be carried out, a complicated exchange of coordinates is necessary, and a hydraulic unit which occupies a relatively wide space is required. For these reasons, even in the coating robot, a robot of a so-called increased safety explosion proof assembly driven by a brushless DC servo-motor has been developed.
However, the aforesaid brushless DC servo-motor is merely relatively high in safety as compared with general DC motors and is not a perfect explosion proof assembly. This brushless DC servo-motor can be applied to an explosive atmosphere place of class 3 which is an open working place but cannot be applied to the dangerous location of classes 1 and 2 such as enclosed rooms.
In addition, such a brushless DC servo-motor has a great inertia and is not suitable for a coating robot which greatly varies in acceleration and deceleration, thus giving rise to a great energy loss.
Japanese Patent Application Laid-Open Nos. 25695/85, 54758/85 and 54759/85 disclose the art of a so-called ventilation type internal pressure explosion proof assembly in which an electric motor is encased in a motor unit provided in an arm of a motor robot, and an air supply hose and an air discharge hose are connected to the motor unit so that fresh air is fed into the motor unit through the air supply hose and is finally discharged out of the motor unit through the air discharge hose. However, in the ventilation type internal pressure explosion proof assembly, each motor unit must be provided with an air supply source. Since this assembly is of the ventilation type, a large-capacity air supply source is required to maintain pressure within the motor unit at a level above atmospheric pressure, and air consumption is also great.
Furthermore, the prior art construction has a disadvantage in that a pressure detector has to be provided for each motor unit due to unevenness of pressures in the motor units.